This invention relates to a blood oxygenator, particularly of the membrane type.
Blood oxygenators are exemplified by U.S. Pat. No. 4,376,095 to Hasegawa, U.S. Pat. No. 4,556,489 to Diettrich, Jr. et al, U.S. Pat. No. 4,620,965 to Fukusawa et al, U.S. Pat. No. 4,631,053 to Taheri, U.S. Pat. No. 4,639,353 to Takemura et al, U.S. Pat. No. 4,645,645 to Martinez et al, and U.S. Pat. No. 4,722,829 to Giter.
Two types of blood oxygenators are the inside perfusion type, in which blood is passed through the bores of tubules, while gas is passed on the outside of the tubules, and the outside perfusion type, in which gas is passed through the bores while blood is passed on the outside of the tubules. Blood oxygenators of the outside perfusion type advantageously provide for more uniform gas distribution than inside perfusion oxygenators, and for turbulent blood flow. Turbulence retards flow, thereby increasing gas exchange.
Fukusawa et al and Takemura et al illustrate hollow fiber membrane, blood oxygenators of the outside perfusion type.
In many conventional blood oxygenators, a cylindrical housing is packed with a bundle of hollow fibers in such a way that the hollow fibers are parallel to the longitudinal axis of the housing. However, as explained at column 1, line 68 through column 2, line 2 of Takemura et al, blood oxygenators of such construction have a low gas exchange rate per unit area of the hollow fiber membrane.
By comparison, as exemplified by Takemura et al, blood oxygenators in which the hollow fibers are disposed within a blood chamber so as to be non-parallel to the direction of blood flow, can produce more turbulent blood flow and thus improved oxygenation. By "direction of blood flow" is meant for purposes of this description, the general direction of blood flow within a blood chamber between the blood inlets and outlets.
In many conventional blood oxygenation systems, a pump is disadvantageously located on the blood inlet side of the oxygenator, between the patient and the blood oxygenator. However, as exemplified by Fukusawa et al, a pump may be avoided by utilizing the head developed between the patient and the oxygenator.
A further problem with conventional blood oxygenation systems is the large priming volume required. The greater the priming volume, the greater the dilution of a patient's blood. A lowered hematocrit results from dilution. In the case of an infant or child, the amount of blood available for filling a blood oxygenation system, is particularly small and the dilution problem is as a result exacerbated.
Martinez et al provide an oxygenator with reduced priming volume in the heat exchanger section. Diettrich, Jr. et al and Giter describe a reduced oxygenator priming volume. Fukusawa et al disclose a reduced priming volume as an inventive object, and show, for instance, in FIG. 17 thereof, a heat exchanger in a blood reservoir.
However, there continues to be a need for an improved blood oxygenator, in particular an oxygenator having reduced priming volume. Beneficially, such an improved oxygenator would be characterized by improved oxygenation, and would better utilize the head developed between a patient and the oxygenator.